FIGS. 14, 15, and 16 are section views illustrating different types of conventional disc-rotating motors. In a growing demand for reducing the thickness and size of a disc-driving unit, manufacturers conventionally have employed the structures shown in FIGS. 14 through 16 for a drop-guard mechanism that protects a rotor from coming out of the motor of a disc-driving unit.
As shown in FIG. 14, a conventional disc-rotating motor has rotor 101 and stator 102. Rotor 101 has shaft 121, and has downwardly protruded engaging member 104 under turntable 103. On the other hand, stator 102 has bearing housing 105 for holding bearing 122 that supports shaft 121. Bearing housing 105 contains engaged member 106. An axial engagement between engaging member 104 and engaged member 106 prevents rotor 101 from coming out of stator 102. The axial direction mentioned above is the direction along shaft 121.
Here will be described how engaging member 104 engages with engaged member 106 in the aforementioned structure.
Inserting shaft 121 of rotor 101 in bearing 122 of stator 102 allows engaging member 104 of rotor 101 to make a contact with engaged member 106 of bearing housing 105, thereby urging engaging member 104 in a radial direction. With the application of force, engaging member 104 has an elastic deformation and reaches under engaged member 106. Even if rotor 101 undergoes an upwardly applied force with respect to shaft 121, engagement between engaging member 104 and engaged member 106 can protect rotor 101 from coming out of stator 102.
The engaging method as described above has been introduced in some suggestions. In a suggestion, a resin-made or a metal-made drop-guard member, which is integrally disposed on a turntable, engages with a bearing housing. In another suggestion, elastic metal disc is fixed on a synthetic resin-made turntable. An arm-like engaging latch is integrally formed with the metal disc so as to engage with a bearing housing. Such structures are disclosed, for example, in Japanese Patent Unexamined Publication No. H09-247886 and in Japanese Patent Unexamined Publication No. H10-23702.
Another conventional disc-rotating motor shown in FIG. 15 is formed of rotor 107 and stator 108. Drop-guard member 110 with a helical groove is attached to turntable 109 of rotor 107. Drop-guard member 110 is made of a material different from that of turntable 109. A helical groove as a counterpart to be engaged with the groove of drop-guard member 110 is formed on holder 112 disposed on stator core 111 of stator 108, or on bearing housing 113 of stator 108.
When shaft 123 of rotor 107 is inserted in bearing 124 of stator 108, tightly fitting the helical groove of drop-guard member 110 with the counterpart helical groove of holder 112 or of bearing housing 113, while rotating rotor 107, completes the assembly of the motor. The structure above protects rotor 107 from coming out of stator 108. For example, Japanese Patent Unexamined Publication No. H08-51740 introduces the aforementioned structure.
FIG. 16 shows a still another conventional structure of a disc-rotating motor, which is formed of rotor 114 and stator 115. Drop-guard washer 116 is fixed at shaft 117 of rotor 114. That is, shaft 117 and drop-guard washer 116 are integrally disposed on rotor 114. If rotor 114 undergoes an upwardly applied force with respect to shaft 117, washer 116 hits against bearing 118 of stator 114, thereby protecting rotor 114 from coming out of stator 115.
Modifications may be made in the structure above such as, forming the washer into a specific shape with elasticity so that the rotor can be removed from the stator as necessary. For example, such a washer is disclosed in Japanese Patent Unexamined Publication No. 2003-18788.
In recent years, a disc-rotating motor for a disc-driving unit has to meet a wide range of demands-not only reduction in size and thickness, but also longer life (as long as several thousands hours) and higher reliability against exchanging discs as many as several tens of thousands times.
Besides, in terms of environmental protection, an effective use of resources and an environment-friendly disposal method have become an important issue. It is therefore preferable that the motor should be easily repaired, recyclable, disassembled, and classified for recycling or disposal.
In the drop-guard mechanism shown in FIG. 14, however, engaging member 104 and engaged member 106 are required to have a shape that can be elastically changed, or to be made of a material that permits an elastic change. Such a deformable design does not seem to be appropriate from the point of giving a disc-rotating motor greater durability against exchanging discs several tens of thousands times.
As described earlier, rotor 101 cannot be removed from stator 102. If possible, due to an excessive elastic deformation, break down or plastic deformation of engaging member 104 and engaged member 106 will the result. Furthermore, due to reduction in size and thickness of the product, the drop-guard mechanism has to be designed in a limited space, and accordingly, a high accuracy of components is required. Such structured disc-rotating motor is therefore not reusable.
In contrast, the drop-guard mechanism of FIG. 15 has an advantage that rotor 107 is easily removed from stator 108. However, the need for keeping a length in an axial direction arises from the structure in which a helical groove is formed in drop-guard member 110. The structural constraint is an obstacle to a disc-rotating motor formed into a compact and low profile body. Forming a helical groove needs a high accuracy, and therefore the member, on which a helical groove to be formed, should be a metallic member processed by cutting operations, or should be a resin-molded member. The limited material selection has less advantage in reducing production cost.
According to the drop-guard mechanism of FIG. 16, rotor 114 can be removed from stator 115. In addition, the mechanism can be easily established by only washer 116 fixed to shaft 117, whereby the production cost is kept relatively low. As shown in FIG. 16, the drop-guard mechanism is disposed under bearing 118. Keeping a length under bearing 118 is, too, an obstacle to further reduction in size and thickness of a product. Besides, the structure is not suitable for pursuing reliability in a long life of a product.